I. Field of the Invention
The present invention relates generally to the field of tie-down rollers for car carrier trucks and trailers. In particular, it relates to preventing a tie-down roller from disengaging or dislodging and allowing cars being carried to impact against each other, to impact against structural members of car carriers or to fall off of carriers. It provides safety against damage to cars from over tightening tie-down chains. It also protects against wear that weakens tie-down rollers and causes structural hazards.
II. Description of the Prior Art.
Tie-down rollers are a form of a manual winch for winding a tie-down chain tightly to hold cars on car carrier trucks and trailers. There is a tie-down roller at each car wheel portion of hydraulically positional wheel ramps. Typically, a tie-down roller has a tie-down bar that is provided with a dry bearing at each side of the ramp at a car wheel position. A tie-down chain is hooked to each of four corner tie-down brackets under a car and then wound around an inside end of each of four tie-down bars separately. The chain is wound by hand wrench rotation of the tie-down bar at an outside end of the tie-down bar. At the outside end of each tie-down bar where it can be reached from outside of the car carrier and from outside of each car being carried, there is a ratchet wheel with a pawl pivotally positioned to fall between ratchet teeth to prevent the tie-down chain from unwinding and becoming loose.
Too often, however, the tie-down chains "settle into" each other and for various other reasons lose tightness. Sometimes tightness is lost only momentarily and at other times progressively when cars being carried bounce due to particularly uneven or bumpy road conditions. When looseness occurs, the ratchet pawl can be disengaged totally and render a particular tie-down roller ineffective. Excessive tightening of the tie-down chain to prevent loosening can distort framework of cars in the vicinity of tie-down brackets. There are precautions to prevent such loosening without excessive tightening. One is to assure that all twisting is removed from a chain before it is tightened. But even the best and most cautious workers sometimes make mistakes that result in loosening of the tie-down chains.
A spring to hold the pawl in contact with the ratchet teeth has been tried previously. It worked, but not for long. It was broken and became dislodged soon because it was positioned where it came in contact with working conditions.
Short wrench handles have been tried to prevent over tightening of the tie-down chains. But different types of cars require different tightness and different individuals have different strength to rotate the tie-down bar with a wrench handle. Some individuals jump on the handles with their entire weight to rotate the tie-down bars. This is an inaccurate method because different individuals have different weight and ability to jump on the wrench handle. Obviously, too much tightening of the chains will result in distortion of the vehicle undercarriage with disastrous results.
Loose dry bearings are used generally for both ends of the tie-down bar. But wear occurs due to insufficient wear resistance of materials used. Soft bearings such as nylon were tried but quickly came off, leaving the mechanism in a hazardously wearing condition.
Another problem which has plagued the industry in the past, is the safety aspect of the operator having fingers and hands caught in the tie-down mechanism when it begins rapidly release the load attached to it. Obviously, the results will be a severe injury to the operator.